1. Field of the Invention
The present invention relates to an automotive air induction duct, and more particularly to an automotive air induction duct in which a strut portion is improved which is provided as a so-called reinforcement rib which secures a rigidity required to resist a manifold air pressure of the like.
2. Description of the Related Art
An automotive air induction duct is such as to increase the combustion efficiency of an engine so as to increase the output of the engine by supplying outside air taken into from the outside to the engine via an air cleaner. The automotive air induction duct is sometimes placed so that an air induction opening, which is made to open towards a front of the vehicle, is positioned within a space defined between a hood (a bonnet, a hood panel) and an upper radiator support at a front part of a vehicle body in order to take in outside air efficiently while the vehicle is running.
Manifold air pressure (a negative pressure generated when the internal pressure in the induction duct becomes lower than the atmospheric pressure by virtue of vacuum) is exerted on the automotive air induction duct when outside air is taken thereinto in association with the start of the engine. Due to this, unless the induction duct has a rigidity which can bear the manifold air pressure so exerted, the upper duct wall portion and the lower duct wall portion are deformed in such a manner as to approach each other, and in the worst case, there is caused a risk that the induction duct is deformed to be collapsed, whereby the air induction opening is closed. As this occurs, a required amount of outside air cannot be introduced into the engine, leading to the occurrence of a problem that the output of the engine is reduced.
In addition, in case hot air within an engine compartment is taken into the air induction duct, the inherent function of the air induction duct to supply a predetermined amount of air for the engine cannot be fulfilled, calling for a reduction in combustion efficiency. To cope with this, there sometimes occurs a case where a sealing mechanism for preventing the suction of hot air into the induction duct is provided in a space defined between the hood and the upper duct wall portion. With the seal member provided on the hood side like this, however, in the event that an external load is exerted on the hood, the load so exerted is exerted, in turn, on the upper duct wall portion via the seal member. As this occurs, in case the air induction duct is deformed when such an external load that is to be exerted by, for example, the hand of a human being is exerted on to the hood, the engine performance is also affected. Due to this, a rigidity is required for the air induction duct which can bear such an external load that is to be exerted by, for example, the hand of a human being even when the load is actually exerted on to the hood. Consequently, a countermeasures is on demand for the automotive induction ducts against an easy deformation of the upper duct wall portion by virtue of the manifold air pressure and the external load exerted from the hood via the seal member.
On the other hand, in recent years, safety measures to protect pedestrians have been required to be established, and to meet this requirement, a pedestrian injury reduction body has been under development in which when a running vehicle happens to erroneously collide against a pedestrian, an impact generated by the collision can be absorbed by virtue of a proper deformation of the body of the vehicle such as the hood. In the pedestrian injury reduction body like this, in order to realize effectively the alleviation of the seriousness of an injury that the pedestrian is to suffer from by virtue of absorption of the impact, the air induction duct lying below the hood via the sealing mechanism has to be such as to permit a proper depressed deformation of the hood when colliding against the pedestrian. Note that in the event that the sealing mechanism is not provided in the space defined between the hood and the air induction duct, it is understood that the permitted deformation amount of the hood is increased by such an extent that the sealing mechanism does not exist. However, the limited space within the engine compartment makes it difficult to secure a large space between the hood and the upper duct wall portion. Due to this, even in a case where the sealing mechanism is not provided, since, in case the hood is deformed, the hood is brought into abutment with the upper duct wall portion substantially at the same time, the air induction duct also has to be such as to permit a proper deformation of the hood.
Then, there are known automotive air induction ducts which permit a proper deformation of the hood as in the case of an accident such as a collision while normally realizing the increase in rigidity so as to resist the manifold air pressure or the like (for example, refer to JP-A-2004-124757 (FIGS. 1, 2, 6, 8), JP-A-2004-183514 (FIGS. 1, 3, 5, 7)).
The automotive air induction duct disclosed in JP-A-2004-124757 is such as to be molded from a resin material and is, as shown in FIG. 7, made up of an upper duct wall portion 81 disposed close to a back side of a hood of a vehicle, a lower duct wall portion 83 which is disposed to oppositely face the upper duct wall portion 81 at such an interval as to secure a required space therebetween so as to form together with the upper duct wall portion 81 an air induction opening which is made to open towards a front of the vehicle and an air induction passageway which supplies outside air taken into from the air induction opening for an engine, and a support wall portion 85 as a support portion which rises integrally from the lower duct wall portion 83 in such a manner that a flat surface-shaped support portion 84, which is a raised distal end surface, is joined to a back side of the lower duct wall portion 83 by virtue of fusion bonding so as to support the upper duct wall portion 81. In addition, a breakage expectation line 86 is provided at an area where the support wall portion 85 continuously connects to the lower duct wall portion 83 in such a manner as to surround the support wall portion 85. This breakage expectation line 86 is constituted by a plurality of thinned portions 87 provided rectilinearly at required intervals at the continuously connecting area of the support wall portion 85 to the lower duct wall portion 83 (or by a thinned portion provided to extend rectilinearly along the full circumference of the continuously connecting area).
In this automotive air induction duct, when the hood is deformed downwards as a result of a collision with a pedestrian, whereby the upper duct wall 81 is depressed from above together with an impact force, the support wall portion 85 receives the pressure from the upper duct wall portion 81 at the flat surface-shaped support portion 84 and is then depressed downwards without being subjected to a buckling deformation thereof. As this occurs, since a stress by the pressure is exerted on to the thinned portion 87 which forms the breakage expectation line 86, a breakage is generated along the breakage expectation line 86, and the support wall portion 85 is separated from the lower duct wall portion 83 and is allowed to move downwards. As a result, a further deformation of the hood is permitted along with the sinking of the upper duct wall portion 81.
In addition, the automotive air induction duct disclosed in JP-A-2004-183514 is such as to be molded similarly from a resin material, has the same basic configuration as the automotive air induction duct disclosed in JP-A-2004-124757 and is, as shown in FIG. 8, made up of the upper duct wall portion 81, the lower duct wall portion 83 and a support wall portion 85 having the flat surface-shaped support portion 84. Then, oppositely facing side wall portions of the support wall portion 85 are bent at an intermediate location thereof, so that the side wall portions are each made up of a primary support portion 88 which is situated on an upper duct wall portion 81 side and which extends at a primary inclined angle α relative to a vertical direction and a secondary support portion 89 which continuously connects to the primary support portion 88 in a bent fashion so as to be situated on a lower duct wall portion 83 side and extends at a secondary inclined angle β which is larger than the primary inclined angle α. Namely, the side wall portions of the support wall portion 85 is flared from a distal end side to a proximal end side thereof, and the degree of flare of the secondary support portion is made larger than the degree of flare of the primary support portion 81.
In this automotive air induction duct, similar to the automotive air induction duct disclosed in JP-A-2004-124757, when the hood is deformed downwards as a result of a collision with a pedestrian, whereby the upper duct wall 81 is depressed from above together with an impact force, the flat surface-shaped support portion 84 of the support wall portion 85 receives the pressure so exerted on the surface thereof. The support wall portion 85, in which the pressure is received by the flat surface-shaped support portion 84, is folded further in such a manner that the bent portions on the side wall portions approach each other and is deformed into a curved shape in such a manner that the primary support portion 88 expands outwards, whereby the support wall portion 85 is deformed into a collapsed state where the support wall portion 85 is entirely collapsed. As a result, a further deformation of the hood is permitted along with the sinking of the upper duct wall portion 81.
Note that both FIGS. 7 and 8 are sectional views showing cross sections of flow paths of air induction passageways 82 (sectional views taken along planes normal to an air flow direction in which outside air taken into from the air induction opening flows inside the air induction passageway) and that in the automotive air induction ducts disclosed in Patent JP-A-2004-124757 and JP-A-2004-183514, the external shape of the cross section of the support wall portion 85 on the cross section of the flow path of the air induction passageway 82 is formed substantially into a trapezoidal shape. In addition, both the automotive air induction ducts are such as to be molded by virtue of blow molding, and the back side of the upper duct wall portion 81 and the flat surface-shaped support portion 84 of the support wall portion 85 are joined together through fusion bonding.
However, in the related automotive air induction duct disclosed in JP-A-2004-124757, the further deformation of the hood is permitted due to the support wall portion 85, in which the pressure from the upper duct wall portion 81 is received by the flat surface-shaped support portion 84, being broken along the breakage expectation line 86 to thereby be separated downwards from the lower duct wall portion 83. Due to this, after the further deformation of the hood has been permitted so as to absorb the impact generated by the collision with the human being, a hole is formed in the lower duct wall portion 83 due to the breakage of the breakage expectation line 86. As this occurs, since hot air within the engine compartment is introduced into the air induction duct, there may be called for a risk that the engine is caused to fail by the hot air introduced into the air induction duct, for example, when the vehicle needs to be moved after the accident. In addition, the reuse of the lower duct wall portion 83 which now has the hole opened therein becomes impossible.
On the other hand, in the related automotive air induction duct disclosed in JP-A-2004-183514, the further deformation of the hood is permitted due to the support wall portion 85, in which the pressure from the upper duct wall portion 81 is received by the flat surface-shaped support portion 84, being deformed into the collapsed state. In addition, since this support wall portion 85 is deformed into the collapsed state due to the support wall portion 85 being folded further largely in the direction the bent portions on both the side wall portions approach each other when a certain large load is exerted thereon, once the support wall portion 85 is deformed into the collapsed state, it is difficult for the support wall portion 85 to be restored to its original shape (or a shape close to the original shape, and this will be true hereinafter), and even in case the pressure exerted on the support wall portion 85 from the upper duct wall portion 81 is removed, it is considered that the restoration of the support wall portion 85 to its original shape is difficult. Due to this, this automotive air induction duct has a poor reusability once it has been deformed.
In addition, in the support wall portion 85 which has been deformed into the collapsed state, the support wall portion 85 is deformed in the curved shape in the direction in which the primary support portions 88 expand outwards (in a direction in which the cross sectional area of the flow path of the air induction passageway is narrowed). Namely, the deformation of the support wall portion 85 encompasses a deformation which reduces the cross sectional area of the flow path of the air induction passageway 82 (a curved deformation of both the side wall portions). The deformation which reduces the cross sectional area of the flow path of the air induction passageway 82 becomes disadvantageous in supplying a required amount of outside air for the engine. Due to this, there may be called for a risk that the engine is caused to fail due to the lack of air, for example, when the vehicle needs to be moved after the accident.